Short arc lamps provide intense point sources of light for applications such as medical endoscopes, instrumentation, and video projection. Short arc lamps also are used in industrial endoscopes, such as in the inspection of jet engine interiors. More recent applications have included dental curing systems, as well as color television receiver and movie theater projection systems, such as is described in pending U.S. Provisional Patent Application No. 60/634,729, entitled “SHORT ARC LAMP LIGHT ENGINE FOR VIDEO PROJECTION,” filed Dec. 9, 2004, hereby incorporated herein by reference. A typical short arc lamp comprises an anode and a sharp-tipped cathode positioned along the longitudinal axis of a cylindrical, sealed concave chamber in a ceramic reflector body that contains xenon gas pressurized to several atmospheres. Descriptions of such arc lamps can be found, for example, in U.S. Pat. Nos. 5,721,465, 6,181,053, and 6,316,867, each of which is hereby incorporated herein by reference. The manufacture of high power xenon arc lamps involves the use of expensive and exotic materials, as well as sophisticated fabrication, welding, and brazing procedures. Reduction in parts count, assembly steps and tooling requirements provides cost savings and improved product reliability and quality.
Exemplary prior art arc lamps are shown in FIGS. 1 and 2. The first lamp 100 comprises an optical coating 102 on a sapphire window 104, a window shell flange 106, a body sleeve 108, a pair of flanges 110 and 112, a three piece strut support assembly 114, a cathode 116, an alumina-ceramic elliptical reflector body 118, a metal shell or sleeve 120, a copper anode base 122, a base weld ring 124, a tungsten anode 126, a gas tabulation 128, and a charge of xenon gas 130. The second lamp 200 comprises a tilted hot minor assembly 201 including a retaining ring 202, a tilted collar 204, a color filter 206, a hot-mirror 208, and a ring housing 210. A tilted land 212 inside the ring housing 210 matches the orientation of the tilted collar 204. The lamp further includes a sapphire window 214 set in a ring frame 216. A single bar strut 218 attaches at opposite points on the bottom of the ring frame 216. A cathode 220 has a slotted end opposite to the pointed arc-discharge end. A body sleeve 222 has a xenon-fill tubulation 224 made of copper tubing. A xenon gas charge 226 is injected into the lamp 200 after final assembly. The lamp also includes a ceramic reflector 228, an anode flange 230, and a tungsten anode 232.
Problems with arc lamps such as these include the relatively large number of parts needed to manufacture the lamps, which increases manufacture time and cost. Also, it can be difficult to achieve the precision alignment needed for the arc gap dimensions to assure consistent lamp operation in these arc lamps. Additional tooling typically is used for alignment, which increases the time necessary for manufacture and increases the probability of damaging a lamp during manufacture.
Various attempts have been made to reduce the number of parts and improve the lifetimes and efficiencies of these lamps. Attempts were made to reduce the number of welds, such as by brazing pieces together, but the materials and brazing techniques available often did not provide the necessary strength for pressurized operation. The types of materials being used and processes for manufacturing components were varied, but often resulted in designs that could not meet the cost target of the intended applications, due to the high costs of materials such as ceramics. Further, components such as a heat conductive mounting that were fabricated from a ceramic material to facilitate high temperature operation had poor heat conduction properties and did not facilitate heat transfer from the enclosed atmosphere. This limit on the operating temperature placed a constraint on the power at which the lamps could be operated.
There also were many attempts to redesign the reflector in order to keep the reflector cool. A conventional reflector is electroformed, with a heat conductive mounting that is built up by electroplating, then machined to the proper size. Alternatively, the reflector can be brazed to a metal heat conductive mounting then machined. These steps require a significant amount of additional machining and cost. Another approach was to machine the reflector directly into the heat conductive mounting, using a machine such as a precision diamond tool lathe. The reflector then is coated with a material such as silver. This still required a significant amount of machining, and the lathe-produced reflector typically had grooves or surface roughness that did not produce an optical reflector.
Due to the increasingly large numbers of xenon arc lamps being produced and marketed, opportunities to save money on the materials, manufacturing, and/or assembly procedures are constantly being sought. Being the low-cost producer in a market typically translates into a strategic competitive advantage.